This invention pertains to a method of controlling an ignition position of an internal combustion engine and an ignition control system for practicing the ignition control method.
An ignition system for an internal combustion engine comprises an ignition circuit to generate an igniting high voltage in a secondary coil of an ignition coil by controlling a primary current of the ignition coil and an ignition control system to control a rotation angle position (an ignition position) where an ignition signal is applied to the ignition circuit.
The ignition control system comprises low speed ignition position control means to control the ignition position of the internal combustion engine so as to ignite the engine when it is detected that the rotation angle position of a crankshaft of the engine is coincident with a peculiar rotation angle position predetermined in accordance with the rotational speed of the engine and steady-state ignition position control means to control the ignition position of the internal combustion engine so as to ignite the engine when the ignition position arithmetically operated under the control condition of at least the rotational speed of the engine. The ignition position of the engine is determined by the low speed ignition position control means when the engine should start or is rotating at the rotational speed of a set value or less than and by the steady-state ignition position control means when the engine is rotating at the rotational speed exceeding the set value.
On the internal combustion engine, a signal generator device is mounted to obtain an engine information such as a rotational speed information and a rotation angle information. The signal generator device comprises a conventional inductor type generator which generates a first pulse signal at a first rotation angle position set at a position advanced relative to a top dead center of the engine corresponding to the rotation angle position of the crankshaft when the piston reaches the top dead center and generates a second pulse signal at a second rotation angle position set at a position delayed relative to the first rotation angle position.
The first rotation angle position is normally set at the maximum advanced position of the ignition of the engine or at the position further advanced relative to the maximum advanced position and the measurement of the ignition position is made with the first rotation angle position as the reference position. The second rotation angle position is set at the position suitable for the low speed ignition position.
In the conventional ignition control apparatus, the low speed ignition position control means is adapted to apply the ignition signal to the ignition circuit when the aforementioned signal generator device generates the second pulse signal at the second rotation angle position suitable for the low speed ignition position.
The steady-state ignition position control means comprises ignition position arithmetical operation means to arithmetically operate the ignition position by obtaining the rotational speed information of the engine and the rotation angle information thereof from the signal generated at the steady position by the signal generator device mounted on the engine, for example and ignition signal generation means to start the measurement of the ignition position which is obtained by the arithmetical operation when the signal generator device generates the peculiar signal and to generate the ignition signal when the measurement of the ignition position is completed (when it is detected that the rotation angle position of the crankshaft of the engine is coincident with the ignition position obtained by the arithmetical operation). These means may be accomplished by practicing a predetermined program in a microcomputer, for example.
It will be considered that the ignition position may be controlled so as to ignite the engine at the ignition position given by the arithmetical operation by using the rotation information obtained from the output of the signal generator device. However, the rotation information cannot be positively obtained from the signal generated by the signal generator device because of the fine variation in the rotational speed of the crankshaft caused by the variation in stroke of the engine due to the unsteady rotation of the engine when the engine should start or while the engine is rotating at the low speed. Thus, it is hard that the low speed ignition position is accurately obtained and if the engine tried to be ignited at the arithmetically operated ignition position, the rotation of the engine gets further unsteady. Thus, when the engine is rotating at the low speed, it has been ignited not by the arithmetically operated ignition position, but by the signal generated at the rotation angle position predetermined by the signal generator device.
In some cases, the ignition position of the engine is advanced relative to the top dead center when the engine should start, it will fail to start due to the phenomena that the piston of the engine is forced backward when the engine is ignited. Therefore, the engine is required to be ignited at the position fully delayed relative to and closer to the top dead center.
However, as the low speed ignition position is set to be fully delayed relative to the top dead center to prevent the piston of the ignited engine from being forced backward, in some cases, the idling rotation of the engine tends to be unsteady due to the excessive delay of the ignition position when the engine reaches the idling rotational speed after it starts.
In some internal combustion engines, for instance, the appropriate ignition position when the engine should start is a position delayed by 2 degrees relative to the top dead center while the appropriate ignition position in the idling condition is a position advanced by 10 degrees relative to the top dead center. In this case, if the low speed ignition position is set at the position where it is delayed by 2 degrees relative to the top dead center in view of the good startability of the engine, then the idling rotation of the engine cannot be made in a steady manner.
Although it is considered that the idling ignition position is determined by the arithmetical operation, it cannot be arithmetically operated in a positive manner due to fine variation of the rotational speed of the engine as aforementioned and therefore the rotation of the engine cannot be made in a steady manner even though it is ignited at the arithmetically operated ignition position.
Although it will be considered that three or more than three signals are generated at different positions by the signal generator device and the starting and idling ignition positions may be determined by using these signals from the signal generator device, the construction of the signal generator device for generating three or more than three signals will be complicated.
Accordingly, it is a principal object of the invention to provide an ignition control method for an internal combustion engine adapted to set the appropriate ignition positions when the engine should start and when it rotates at the low speed.
It is another object of the invention to provide an ignition control system for an internal combustion engine adapted to set the appropriate ignition positions when the engine should start and when it rotates at the low speed.
In order to accomplish the object of the invention, the present invention is provided with a signal generator device to generate a first pulse signal at a first rotation angle position set at a position advanced relative to a top dead center of an internal combustion engine and a second pulse signal at a second rotation angle position set at a position delayed relative to the first rotation angle position and a position detection circuit to output a position detection signal whenever a peculiar or specific point of a waveform of an output from a generation coil of a magneto AC generator driven by the engine and a phase relation between the output of the signal generator device and the output of the generation coil is so set as that the position detection signal is generated at least once between the first and second rotation angle positions.
The ignition control system of the invention controls the ignition system of the engine so that while the rotational speed of the engine is lower than a set value, the engine is ignited when one selected among the second pulse signal and the position detection signal is generated and so that while the rotational speed of the engine exceeds the set value, the engine is ignited at the rotation angle position arithmetically operated under the control condition including the rotational speed of the internal combustion engine.
What is meant by xe2x80x9cthe peculiar point of the waveform of the output from the generation coil of the magneto AC generatorxe2x80x9d is the point apparently distinguishable from the other points which may be a zero cross point or a peak point, for example. In case that the position detection signal is generated when the peak point of the output voltage of the magneto AC generator is detected, a peak detection circuit may be used for the position detection circuit. In case that the position detection signal is generated when the zero cross point of the output voltage of the magneto AC generator is detected, a zero cross detection circuit may be used for the position detection circuit.
Since the position detection circuit generates the position detection signal whenever the peculiar point of the waveform of the voltage from the generation coil is detected, a plural of position detection signals are generated every one revolution of the crankshaft of the engine, but since the invention uses the position detection signal generated after the signal generator device generates the first signal, for the signal determining the low speed ignition position, the position detection signal used for determining the low speed ignition position can be easily distinguished among the plural of the position detection signals generated per one revolution.
As aforementioned, as the rotation angle position information of the engine is obtained from the waveform of the output of the magneto AC generator driven by the internal combustion engine as well, a plural of signals used for determining the starting ignition position and the low speed ignition position can be generated without any complicated construction of the signal generator device and therefore the low speed ignition position can be positively controlled.